And states that the issue was not on their end but the product of Activision not providing cross-platform support. Cross-platform support that would ensure one PC program could talk to another, something that Microsoft has been actively pursuing in recent times. And really, not that hard to pull off. As in, it's the same format just a different store.
The issue with the most recent Call of Duty has made headlines mainly because PC sales for the title have been lower than expected, with Windows 10 players being unable to find multiplayer matches that had more than a handful of people. On Steam the player count is healthy enough, which is why Microsoft is offering up refunds to anyone who asks for one.
It's a strange turn of events, but also one that highlights the pressure on Microsoft to ensure that the Windows 10 Store appeals to a broad range of gamers. Because outside of first-party titles, it's more reminiscent of a mobile app store than a storefront where one would purchase the latest Call of Duty.
If anything this will serve as a lesson for future releases across both Steam and the Windows 10 Store -- all multiplayer functionality should support cross-play. Either that or remain Steam or Windows 10 only.